I think Lowry would work well alongside Rondo (edit: because Lowry is more of a scoring PG [and a tough defender] so Lowry generally functions quite well in two PG backcourts). As a backup PG/SG. Spread out the floor and let those two pick defenses apart with their ball-handling and driving.
Maybe a (small) three guard backcourt with Avery Bradley. Lots of quickness, toughness and defensive tenacity. Speed up the tempo. Lowry providing another dribble drive threat and scoring ability off the dribble. Plus he has a three point jump shot.
Edit: Meh, nevermind. Lowry's contract demands would be too high for that work out. What was he meant to be asking for, again? $10-12 million a year? That wouldn't work out.